1. Field of the Invention
The present invention relates to diffusion and, more specifically, to a device that is used in a system that injects fluid into a liquid.
2. Description of the Prior Art
Gas diffusers are employed in a variety of applications. One important application addresses the aeration of waste water. Water stored in tanks in waste processing plants includes large volumes of sludge, and typically, includes naturally occurring bacteria which injest the sludge to aid in the decomposing of the sludge. The bacteria are aerobic, which means that they require air to remain alive. Therefore, it is desirable to dissolve air into the water to maintain the bacterial population at an appropriate level.
Bacteria begin to die when air is not continually dissolved in the water. The dead bacteria release nitrogen products, such as ammonia, which dissolve in the water. This process is called nitrification. Conversely, bacteria reproduce and increase in population when air is dissolved in the water resulting in a decrease in dissolved nitrogen products. This process is called denitrification.
Some methods of biological waste water treatment employ aeration systems that have the flexibility of intermittent operation to meet fluctuating requirements. Biological systems that require a denitrification stage with preceding or simultaneous nitrification stages occurring in separate tanks can experience considerable process advantages if the tanks can furnish interchangeability for each zone. The speed of nitrification is subject to sharp fluctuations dependent upon the age of the sludge, pH and temperature. During peak winter loads the degree of nitrification will be reduced unless the nitrification zone is increased. Denitrification takes place after ammonia has been converted to nitrate through nitrification. If there is a decrease in the degree of nitrification, it is recommended that the nitrification zone be increased at the expense of the denitrification zone to achieve maximum processing. An aeration system in individual tanks that can be turned off and on adjusts the effectiveness of both zones. The ability to reduce or completely shut down individual sections of or the total aeration system at low flow, primarily at night, enhances operating economy through energy conservation.
One device currently used to aerate water is manufactured and marketed by the assignee of the present invention under the mark "ROEFLEX Diaphragm Diffuser." The ROEFLEX Diaphragm Diffuser is an upwardly facing convex plastic (polymid) dish which functions as a gas channeling device, and is covered by a highly elastic plastic (EPDM) diaphragm. The diaphragm has a multiplicity of perforations designed to furnish maximum oxygen transfer. When air pressure is applied to the dish, the diaphragm lifts and stretches thereby opening the multiple perforations to allow air to pass through the diaphragm in the form of fine bubbles. When the air pressure is shut off, the diaphragm retracts, thereby sealing the perforations against the surface of the dish below the diaphragm. Also, the retraction of the diaphragm seals the opening in the dish where the air is introduced below the diaphragm, since that portion of the diaphragm directly over the gas supply port is nonperforated. The diaphragm is secured to the dish by its own elasticity.
While the ROEFLEX Diaphragm Diffuser is effective to aerate waste water, it requires relatively high air pressure to be functional. The diaphragm is initially raised and stretched by gas, typically issuing from the gas port and pressing against the non-perforated portion of the diaphragm. The force exerted against that portion of the diaphragm is equal to the gas pressure in the gas port multiplied by the cross-sectional area of the port. Since the gas port in the dish has a relatively small cross sectional area, a relatively high air pressure is needed to raise the diaphragm. It is not practical to increase the cross sectional area of the entire gas port since this would increase the volume of air needed to be pumped, considering the large number of diffusers commonly required for proper aeration.
The present invention overcomes the need for increasing the air pressure in the gas port by increasing the effective area over which, the air presses against the diaphragm, with little increase in needed air volume. The preferred embodiment of the present invention provides a cylinder which surrounds the gas port and extends a few millimeters from the surface of the dish. The cylinder is of a larger diameter than the gas port, thereby increasing the surface area on the diaphragm upon which the gas presses to raise the diaphragm from the surface of the dish. However, the height of the cylinder is relatively small, and the gas volume is only sightly increased. Therefore, more force is exerted on the diaphragm due to the increased surface area without substantially increasing the volume of air required. Also an improved seal between the diaphragm and the gas port is provided, which provides more protection against seepage of the waste water into the gas port.
U.S. Pat. No. 1,642,051 discloses an aerator for flotation ore separators. The aerator employs a rubber mat having a plurality of perforations. A tube is positioned below the rubber mat. The tube supplies air below the mat and the air is diffused into the medium above the mat.
U.S. Pat. No. 2,038,451 discloses a device for aerating fermentation liquids, which employs a porous copper plate through which air is diffused into liquid.
U.S. Pat. No. 3,953,554, discloses a diffuser for aeration systems. The diffuser includes a spherical valve which controls the discharge of air from the diffuser. The upper surface of the diffuser also includes a small number of relatively large holes for diffusing air into water.
U.S. Pat. No. 3,997,634 discloses a diffuser assembly. The assembly employs a flexible diaphragm which defines a plurality of holes for discharging air into water. A spherical valve controls the flow of air to the diaphragm.
U.S. Pat. No. 4,007,240 discloses supporting arrangements for porous diffusers, including a porous diffuser which is positioned over a supporting body. The diffuser is clamped to the supporting body by means of a bolt which passes through a hole in the center of the diffuser, and employs a membrane with a gas impermeable center while this patent employs a membrane with a large hole in the center.
U.S. Pat. No. 4,581,137 discloses a gas diffuser tube assembly. The assembly employs an elongated support member around which is positioned a flexible membrane for diffusing air into liquid. The patent discloses, in FIGS. 9 and 10 and column 5, lines 12 through 19, that the openings 26 in the support member may include somewhat conically shaped shoulders 27 which project away from the support and against the surface of the membrane. The shoulders act like a valve seat for the membrane.
U.S. Pat. No. 4,631,134 discloses a process for the intermittent aeration of liquids and aeration devices for use in such a process. This patent discloses an aeration device which includes an elastic, perforated diaphragm with a central opening through which an air port projects.